an investigative behavior during which an animal elevates its head and curls back its upper lip. this is to detect weaker, fluid-borne pheromones, such as those present in vaginal secretions or urine. curling the upper lip will close off the nostrils and allow the pheromones to enter the nasopalatine duct. from there they travel to the vomeronasal organ and are examined by sensory neurons.

this behavior is exhibited most often by males as a part of courtship behavior, in order to determine whether a nearby female is in estrus and therefore receptive to mating. however, flehmen is also sometimes exhibited by females. this could be during sexual encounters with males, when near another female in estrus, or when introduced to new compounds such as placental fluids or newborn animals.

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